After my research, VMPS is looking very good right now. SVS might be too intrusive in my room, but it is second. Velodyne and HSU are out of my price range for the performance I am looking for. Adire, well, I don't really feel like assembling my own sub if I can buy one ready made, however I am still looking carefully at their already made subs.

VMPS subs come with two subs and play in stereo. Will this still work even though my receiver has only one mono pre amp sub out?